Method and device for pickling rolled metal, in particular steel strips

ABSTRACT

In a method and device for pickling a rolled metal, in particular, steel strip, the metal strip ( 1 ) is fed to a regulated pickling process. In order to carry out the pickling process not only on the basis of conventional pickling parameters but rather taking into consideration additional parameters from outside of the pickling vat, it is proposed to regulate the pickling process, in addition to the pickling medium parameters, by parameters of the coil ( 2 ) and/or metal strip determined and/or measured before the metal strip ( 1 ) enters the pickling section ( 3 ).

[0001] The present invention relates to a method and device for picklingof a metal, in particular, steel strip fed to a regulated picklingprocess.

[0002] DE 197 43 022 A1 discloses a method of pickling a metal stripbased on a measurement in the displacement direction after the picklingplant and in which according to defect categories, which are determinedby a measuring unit, pickling parameters such as, e.g., temperature ofthe pickling liquid, displacement speed of the metal strip, acid contentin the pickling liquid, metal content, in particular, iron content,strip parameters such as, e.g., material and geometrical dimension, areadjusted. In this respect, the defects can only be subsequentlydetermined as well as a conclusion made as to favorable pickling. Thecontrol system deals only with the pickling plant itself.

[0003] According to another known method (EP-0 482 785 A1), turbulentstreams, which are generated in a pickling container with nozzles, areused. Thereby, an optimal pickling result with a minimal consumption ofa pickling medium can be achieved. This result should be achieved bycontrolling the turbulence of the stream in the pickling mediumdependent on the displacement speed of the to-be-pickled strip. Afar-reaching effect is not to be expected.

[0004] A further method of pickling a rolled strip in a pickling plantis disclosed in EP-0 602 437 B1. The method is based on a particularoperating mode according to which several pickling vats adjoin eachother one after the other. In the pickling vats, an acid-containingpickling medium is sprayed by spraying nozzles arranged on a vatpartially sidewise of, above and below the strip displacement plane,with the nozzles being variably controlled and with the pickling mediumbeing introduced in an arbitrary preselected amount. At that, the acidconcentration, and/or medium temperature, and/or the outlet speed of thepickling medium from nozzles are preselected.

[0005] An object of the invention is to carry out the pickling processnot only on the basis of conventional pickling parameters but rathertaking into consideration additional parameters outside of the picklingvat.

[0006] According to the invention, this object is achieved by regulatingthe pickling process, in addition to the pickling medium parameters, byparameters of a coil and/or metal strip determined and/or measuredbefore the metal strip enters the pickling section. The advantageconsists in that the pickling parameters are so adjusted in advance thatunder- or over-pickling is prevented, in that the acid concentration andthe acid supply are correctly adjusted, whereby the pickling medium iseconomically used, and in that the correct temperature can be calculatedin advance, together with other adjustable pickling parameters. At that,the scale, which is removed after casting, shaping, and annealing, andother coatings are already taken into consideration. The invention alsotakes into consideration the preliminary breaking of the scale (by astretching-bending-straightening leveller), whereby fissures and poresare formed in the scale layer, which increases the surface on which theacid acts. In cases when the scale is removed by an abrasive orhydromechanical treatment, the scale quantity, which is dissolved in thepickling process, is reduced. Thereby, the preliminary descaling permitsto reduce pickling time. In case, the temperature of the metal stripincreases before the strip enters in the pickling section, the contacttime of the strip surface with the pickling medium increases at anoptimal pickling temperatures.

[0007] The heating path of the metal strip is shortened and the picklingtime falls. The pickling time also falls when the scale is removed bylaser-optical means before the strip enters the pickling section, andthe quantity of the to-be-dissolved scale is reduced.

[0008] The method includes preadjustment of the pickling process inaccordance with measured values of a coil effected on a basis of aset-up computation model, and regulating the process on a basis of aregulating computation model that takes into consideration at leastmeasured values for the scale, strip temperature, pickling mediumtemperature, and/or acid concentration. The quantity of the scale, e.g.,needs not to be assessed, as was the case previously. An integration ofthe additional scale calculation model takes place. A target variable ofsuch optimization can be: minimum energy use, variable coil output,acceleration reaction dependent on the surface contamination, minimizingthe consumption of the pickling medium and losses of the picklingmedium, minimizing overpickling, and minimizing underpickling. Withregulated descaling units, measurement units for determining scaling candetermine thickness of the scale layer, shape, distribution and color.To this end, precise calculation models are used.

[0009] According to an embodiment of the invention, the servo componentsof the pickling section are regulated or readjusted based on a measuredvalue for the scale deposit before the pickling section. This makespossible regulation of the pickling section with a least possibletransit time.

[0010] Advantageously, additional measured values for scale deposits orcoating are determined in a region in a displacement direction in frontof the pickling section, and are used for readjustment of the servocomponents of the pickling section and/or dependent on measured and/orcalculated values.

[0011] Other parameters outside of the pickling section are taken intoconsideration by controlling the pickling times based on strip entrancedata of the coil and on the system adjustment.

[0012] In accordance with another method step, the measured values forthe coating or the scale are used for regulation of a pretreatment unitarranged upstream of the pickling section.

[0013] It is advantageous that the pretreatment unit and the servocomponents of the pickling section are readjusted in accordance with themeasured and calculated values.

[0014] In device for pickling a metal, in particular, steel strip fed ina displacement direction from a coil of a pickling plant, for which aregulation by a plurality of parameters is contemplated, the object ofthe invention is achieved by communicating measured values from coilmeasured value or data transducers via a set-up computation model and aregulating computation model to adjustment units of a pickling section.Thereby, the pickling section can be operated with precise regulationwhich results in the above-discussed advantages.

[0015] In one embodiment of the device, it is provided that measuredvalue from coil measured value transducers are input into the regulatingcomputation model. The set-up computation model uses general entrancedata for the metal strip. The scale deposits can be calculated by usinga trial computation model for effecting preliminary adjustment of theslow and rapid servo components of the pickling section or readjustmentin accordance with comparison.

[0016] In another case, the measured values of a measured valuetransducer for coating or scale are used for readjustment of the servocomponents of the pickling section.

[0017] According to other features, a pretreatment unit, the measuredvalues of which are input into the regulating computation model, isarranged upstream of the pickling section. Upon recognition of theexigency and by suitable evaluation of the coil data and the instantsystem set-up, the pretreatment unit can influence the pickling time. Asa pretreatment unit, a heating unit, a mechanical, abrasive,hydromechanical, laser-optical, or oscillating descaler can be used.

[0018] Further improvement is achieved by providing an induction heatingunit between the pretreatment unit and the pickling section. Theinductive preheating of the metal strip takes place before the picklingsection and is used for rapid regulation of the metal strip temperatureand for adjustment of the metal strip pickling temperature.

[0019] The embodiments of the invention are schematically shown in thedrawings and will be explained in detail below.

[0020] The drawings show:

[0021]FIG. 1 a block-diagram of a basic design of a coil and picklingplant with regulation,

[0022]FIG. 2 a first variant of the same block-diagram with a measuredvalue transducer,

[0023]FIG. 3 a second variant of the block-diagram with a pretreatmentunit,

[0024]FIG. 4 a third variant of the block-diagram with a measured valuetransducer and a pretreatment unit, and

[0025]FIG. 5 a fourth variant of the block-diagram with a measured valuetransducer, a pretreatment unit, and induction heating.

[0026] According tot he basic design shown in FIG. 1, a metal strip isfed from a coil 2 into a pickling section 3. At that, coil data 4 from adata transducer 4 a and a data transducer 4 b are introduced into aset-up computation model 6 and/or into a regulation computation model 8and are processed in accordance with the program. In the set-upcomputation model 6 further measured values 7 can be taken intoconsideration. Thereby, the pickling process is regulated, in additionto the pickling medium parameters, before the metal strip 1 is fed intothe pickling section 3, by parameters of the coil 2 and/or the metalstrip 1 which were determined, in the system 5, with servo componentsand/or measured.

[0027] In accordance with a first variant according to FIG. 2, inaddition to the presetting of the pickling medium parameters,additionally acquires measured values, which characterized the coatingor scale and which are determined by a measured value transducer M in ascale registration unit 10, are processed in the regulating computationmodel 8. The pickling process is regulated, respectively (FIGS. 1-5), onthe basis of the set-up computation model 6 with preset measured valuesof the coil 2 and on the basis of the regulating computation model 8which takes into account at least the measured values for the scale,bath temperature, the temperature of the pickling medium and/or acidconcentration. The additional measured values for scale deposits beforethe pickling section 3 are used for regulating or readjusting the servoelements in the system 5.

[0028] In accordance with a second variant represented in FIG. 3 and asuitable evaluation of the coil information 4, a pretreatment unit H,which influences the pickling time, is used. In addition, the slow andrapid servo components of the pickling section 3 are readjusted inaccordance with measured and/or calculated values output by theregulating computation model 8, in particular, taking into considerationthe changed pickling times.

[0029] According to a third variant, represented in FIG. 4, additionalmeasured value of the scale deposits and coatings is determined by themeasured value transducer M of the scale registration unit 10 located infront of the pickling section 3 in the displacement direction 9, and isused for readjusting of the servo components of the pickling section 3and/or in accordance with measured and calculated values. Besides, thepickling times are regulated on the basis of the strip inlet informationof the coiler 2 and the system set-up. The acquired measured values withrespect to coating and scale are used for regulating a pretreatment unitH located upstream of the pickling section 3.

[0030] On the basis of the fourth variant according to FIG. 5, inaddition to the scale registration unit 10 and the pretreatment unit H,an induction heating unit W is provided between the pickling section 3and the pretreatment unit H. The pickling time is defined as a contacttime of a to-be-cleaned surface with the pickling medium necessary for areliable removal of the contamination from the strip 1. The pretreatmentunit H can include a preheating unit in form of the induction heatingunit W.

[0031] The pretreatment unit H basically includes a mechanical,abrasive, hydromechanical, laser-optical, or oscillating descaler. Theinduction preheating of the metal strip by the induction heating unit Wis effected before the pickling section and serves for a rapidregulation of the metal strip and pickling medium temperatures. List ofReference Numerals 1. Metal Strip 2. Coil 3. Pickling Section 4.Coil-data 4a. Data Transducer 4b. Data Transducer 5. System With ServoComponents 6. Set-up Computation Model 7. Measured Values 8. RegulatingComputation Model 9. Displacement Direction 10. Scale Registration UnitM Measured Value Transducer H Pretreatment Unit W Induction Heating Unit

1. A method of pickling a rolled metal, in particular, steel strip fedto a regulated pickling process, characterized in that the picklingprocess is regulated, in addition to pickling medium parameters, byparameters of the coil and/or the metal strip determined and/or measuredbefore the metal strip is fed into the pickling section.
 2. A methodaccording to claim 1, characterized in that the pickling process ispreadjusted, on a basis of a set-up computation model, with measuredvalues of the coil and is regulated on a basis of a regulatingcomputaiton model that takes into consideration at least measured valuesfor scale, bath temperature, pickling medium temperature, and/or acidconcentration.
 3. A method according to claim 1 or 2, characterized inthat servo parameters of pickling are regulated or readjusted based onmeasured values for scale deposits before the pickling section.
 4. Amethod according to one of claims 1 through 3, characterized in thatadditional measured values for scale deposits or coating are determinedin a region in a displacement direction before the pickling section andare used for readjustment of the servo components of the picklingsection and/or in accordance with measured and calculated values.
 5. Amethod according to one of claims 1 through 4, characterized in thatpickling times are regulated based on strip entrance data of the coiland the system adjustment.
 6. A method according to one of claims 1through 5, characterized in that the measured values for the coating orthe scale are used for regulating a pretreatment unit located upstreamof the pickling section.
 7. A method according to claim 6, characterizedin that the pretreatment unit and the servo components of the picklingsection are readjusted in accordance with the measured or regulatedvalues.
 8. A device for pickling a metal, in particular, steel strip fedin a displacement direction from a coil of a pickling plant, for which aregulation by a plurality of parameters is contemplated, characterizedin that measured values from coil measure value or data transducers (4a; 4 b) are communicated via a set-up computation model (6) and aregulating computation model (8) to adjustment units of a picklingsection.
 9. A device according to claim 8, characterized in thatmeasured values from the coil measured value transducers (4 a; 4 b) areinput into the regulating computation model (8).
 10. A device accordingto one of claims 8 or 9, characterized in that measured values of ameasured value transducer (M) related to coating or scale are used forreadjustment of servo components of the pickling section (3).
 11. Adevice according to one of claims 8 and 9, characterized in that apretreatment unit (H), measured values of which are input into theregulating computation model, is located upstream of the picklingsection.
 12. A device according to one of claims 7 through 11,characterized in that an induction heating unit (W), for the strip (1)is provided between the pretreatment unit (H) and the pickling section(3).